Method and apparatus for plasma etching a wafer

ABSTRACT

A plasma etching machine comprises a process chamber defining an interior region and including a bottom wall having an aperture and a block disposed in the aperture and including a longitudinally extending bore. A shaft extends through the bore and includes a spider push rod extending longitudinally therethrough. An internally cooled chuck is coupled to the shaft and disposed in the interior region and cooperates with the shaft to define a chamber. A spider is disposed in the chamber and is coupled to the push rod. A lift mechanism is coupled to the shaft and the push rod so that the spider pushes up on a wafer in response to actuation of the lift mechanism. A wafer clamping mechanism is coupled to the push rod if a mechanical clamp is used. In the case of electrostatic clamp the bias applied to the chuck is coupled with the use of a rotational roller to allow the bias to be applied to the chuck for the duration of the etch process. A RF source is needed for ionization of the gas. If the plasma etching machine has RF power applied through the bottom, then a rotational roller is used for this as well and must be isolated from the electrostatic voltage used to clamp the wafer. A drive motor is coupled to the shaft for rotating the shaft during a plasma etching process.

[0001] The present invention relates to a method and apparatus forplasma etching a wafer and particularly to plasma etching a wafer usinga rotatable chuck. More particularly, the invention relates to aninternally cooled rotatable chuck for use in a plasma etching process.

BACKGROUND OF THE INVENTION

[0002] Plasma etching apparatus for processing wafers is known.Typically, a chuck serves as a lower electrode in a process chamberwhich can be set in a vacuum state. A wafer is placed on and fixed tothe chuck, and then subjected to the plasma etching process. There aretwo commonly used ways of fixing a wafer to a chuck, mechanicalsupporting means such as a clamp, and an electrostatic chuck forattaching a wafer by means of an electrostatic attractive force. Atypical electrostatic chuck includes a metallic base plate that iscoated with a thick layer of slightly conductive dielectric material. Asilicon wafer of approximately the same size as the chuck is placed ontop of the chuck and a potential difference is applied between thesilicon wafer and the base plate of the electrostatic chuck. This causesan electrostatic attraction proportional to the square of the electricfield in the gap between the silicon wafer and the chuck face.

[0003] When the chuck is used in a plasma filled chamber, the electricpotential of the wafer tends to be fixed by the effective potential ofthe plasma. The purpose of the dielectric layer on the chuck is toprevent the silicon wafer from coming into direct electrical contactwith the metallic part of the chuck and shorting out the potentialdifference. On the other hand, a small amount of conductivity appears tobe desirable in the dielectric coating so that much of its free surfacebetween points of contact with the silicon wafer is maintained near thepotential of the metallic base plate; otherwise, a much larger potentialdifference would be needed to produce a sufficiently large electricfield in the vacuum gap between the wafer and chuck.

[0004] During plasma etching of pattern wafers, the plasma raises thetemperature of the wafer to an undesirable level that could damage thewafer. Accordingly, the chuck must be kept as cool as possible. Thecurrent preferred method of cooling a plasma chuck is with conductivecooling of the backside of the chuck through the use of helium. The faceof the chuck generally includes a pattern of grooves in which helium gasis maintained. This gas provides cooling by thermal contact between thewafer and the chuck. To contain the helium at the chuck and prevent itfrom escaping into the reaction, a clamp must be incorporated with thechuck to hold the wafer down.

[0005] In conventional pattern plasma etched apparatus, the chuck isstationary to allow for cooling. Non-uniform etching occurs, however,due to chamber design or process parameters resulting in undesirablefilm thickness deviations. These deviations in film thickness can belocalized or spread across the entire film surface.

SUMMARY OF THE INVENTION

[0006] The present invention overcomes these shortcomings by providingan internally cooled rotatable chuck for use in a semiconductor waferplasma etching apparatus. By rotating the chuck and the wafer in anetching chamber, the effect of the inherent lack or excess of ions dueto chamber design or process parameters can be minimized. The lack orexcess of ions creating the etch can be spread across the entire wafersurface assuring all locations see the same etch parameters.Accordingly, a more efficient process with better film uniformity willbe realized.

[0007] According to the present invention, a plasma etching machinecomprises a process chamber defining an interior region and including abottom wall having an aperture and a block disposed in the aperture andincluding a longitudinally extending bore. A shaft extends through thebore and includes a spider push rod extending longitudinallytherethrough. The shaft is supported for rotation in the bore. Acontroller controls the speed, direction and duration of the shaftrotation.

[0008] An internally cooled chuck is coupled to the shaft and disposedin the interior region and cooperates with the shaft to define achamber. The chuck includes a clamp, either electrostatic or mechanical,for retaining the wafer on the chuck. The wafer can be retained on thechuck in a conventional face up orientation, an upside down orientation,or on its side within the process chamber.

[0009] A spider is disposed in the chamber and is coupled to a spiderpush rod. A lift mechanism is coupled to the shaft and the spider pushrod so that the spider pushes up on a wafer in response to actuation ofthe lift mechanism. A drive motor is coupled to the shaft for rotatingthe shaft during a plasma etching process. A bellows assembly couplesthe shaft end to a coolant source. The lift mechanism includes a liftplate coupled to the bellows assembly, the lift plate and bellowsassembly being movable between a wafer lifting position and a disengagedposition, the spider push rod including a coolant passage incommunication with the chamber and being movable in response to movementof the lift plate and bellows assembly.

[0010] Further according to the invention, a method for plasma etching awafer comprises the steps of coupling a chuck to a pedestal, couplingthe wafer to the chuck, rotating the pedestal, and etching the wafer.

[0011] The present invention to provide a rotatable chuck for use withapparatus for plasma etching a wafer. The invention also provides arotatable electrostatic chuck for use with apparatus for plasma etchinga patterned wafer. The invention further provides a rotatable chuckhaving coolant passages for conveying coolant to the chuck.

[0012] These and other features and advantages of the invention willbecome apparent from the following detailed description of preferredembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a perspective view of a plasma etching apparatusaccording to the present invention;

[0014]FIG. 2 is a side view a plasma etching apparatus;

[0015]FIG. 3 is a front view of the apparatus of FIG. 2; and

[0016]FIG. 4 is a flow chart of a control process for controlling theapparatus of FIGS. 1-3.

DETAILED DESCRIPTION OF THE DRAWING

[0017] A plasma etching machine 10 for use in plasma etching patternwafers is illustrated in FIGS. 1-3. The machine 10 includes a processchamber 12, a mounting assembly 14, a chuck 16, and a pedestal 18coupled to the chamber 12 and mounting plate 14. A drive motor 20 isattached to the mounting assembly 14 for rotating the chuck and pedestal16, 18.

[0018] The process chamber 12 includes a plurality of sidewalls 22 and abottom wall 24 and a dome 30 (FIG. 2) that cooperate to define aninterior region 32. The bottom wall 24 includes a central aperture 34.

[0019] The mounting assembly 14, best seen in FIG. 2, includes avertical member 14 a, a pair of vertically oriented upper gussets 14 band a pair of vertically oriented lower gussets 14 c projectingorthogonally from the vertical plate 14 a, and a pair of horizontallyoriented mounting plates 14 d, 14 e projecting orthogonally fromopposite sides of the vertical member 14 a. The upper gussets 14 binclude flanges extending outwardly from the upper edges thereof forretaining the mounting assembly 14 to the bottom wall 24 of the chamber12. The lower gussets 14 c are attached to, and provide rigid supportfor, the mounting plate 14 d. Mounting plate 14 e supports the drivemotor 20.

[0020] A cylindrical bearing and seal block 36 having a first end 36 aand a second end 36 b is disposed in the central aperture 34. The block36 includes an angular flange 38 extending radially outwardly from thefirst end 36 a. A radially outer surface 40 of the first end 36 a andthe flange 38 cooperate to define a shoulder that engages the centralaperture 34. When so engaged, the flange 38 abuts the bottom wall 24 andextends between the upper gussets 14 b. The flange 38 includes aplurality of bolt-receiving bores 42 evenly spaced around the flange 38,and a plurality of bolts 44 attach the flange 38 to the bottom wall 24.An O-ring 46 is disposed between the flange 38 and the bottom wall 24.The block 36 further includes a central bore 52 extending longitudinallytherethrough for receiving the pedestal 18. The bore 52 includes a pairof annular grooves at the first end 36 a for receiving a pair of O-rings56. O-rings 46 and 56 cooperate to seal the interior region 32. The bore52 further includes an annular recess 58 extending longitudinallyupwardly from the second end 36 b. A pair of bearings 60 a and 60 b aredisposed in the recess 58 and separated by a spacer 62. An annularbearing cap 64, attached to the second end 36 b, retains the bearings 60a, 60 b and the spacer 62 in position. An end play adjustment nut 66threadedly engages the pedestal 18.

[0021] The pedestal 18 includes a cylindrical shaft 72 having a firstend 72 a and a second end 72 b and a circular plate 74 attached to thefirst end 72 a. The shaft 72 includes 3 sections 76, 78, 80. The firstsection 76 extends downwardly from the plate 74 to a first shoulder 76 athat defines the beginning of the second section 78. The O-rings 56 inthe block 36 engage the first section 76. The second section 78 includesa reduced outer diameter and extends downwardly from first shoulder 76 ato shoulder 78 a. The bearings 60 a, 60 b and spacer 62 engage thesecond section 78. A portion of the second section 78 extending from thesecond shoulder 78 a includes threads to engage the end play adjustmentnut 66. A pulley 86 is coupled to the second section 78 adjacent thesecond shoulder 78. A woodruff key 87 rotationally locks the pulley 86to the shaft 72. The third section 80 extends from the second shoulder78 a to the second end 72 b of the shaft 72 and includes a threadedportion adjacent the second shoulder 78 a. A pulley lock nut 88threadedly engages the portion of the treaded third section 80 adjacentthe second shoulder 78 a to axially retain the pulley 86 on the shaft72. Thus, the pedestal 18 is free to rotate in the block 36, but issubstantially axially fixed in the block 36.

[0022] The pedestal 18 further includes a conductive ring assembly 90and a bellows assembly 92 attached to the second end 72 b. Theconductive ring assembly 90 includes a conductive ring 90 a sandwichedbetween a pair of insulators 90 b, 90 c. O-rings provide a seal betweenthe insulators 90 b, 90 c and the second end 72 b and bellows assembly92, respectively, and to the conductive ring 90 a. The bellows assembly92 includes an upper flange 92 a and a lower flange 92 b. A plurality ofmounting bolts 93 extend through aligned apertures in the upper flange92 a, the conductive ring 90 a and insulators 90 b, 90 c to attach thebellows assembly 92 and conductive ring assembly 90 to the second end 72b of the pedestal 18.

[0023] A plunger assembly 94, attached to the mounting assembly verticalplate 14 a, includes a electrostatic bias roller 96, such as a DCroller, that engages the conductive ring 90 a. A high tension wire 98couples the electrostatic bias roller 96 to a voltage source (notshown). An electrostatic lead 98 a extends from the conductive ring 90 ato the chuck 16 to provide electrostatic voltage to the chuck 16,causing the chuck 16 to become an electrode. An annular lip 16 b,preferably made from a thin film insulator, extends around the peripheryof the chuck 16. The lip 16 b retains the wafer in a spaced relationshipwith the electrostatically charged chuck 16 and prevents the wafer fromcontacting the chuck 16.

[0024] A pneumatic lift actuator 104 is attached to the horizontalmounting plate 14 e and includes air lines 104 a, 104 b and a liftpiston 106. A lift piston 106 engages a lift plate 108 that engages thelower bellows flange 92 b. The lower flange 92 b includes acircumferential groove formed in the radially outer surface thereof. Apair of thrust washers 110 a, 110 b are disposed in the circumferentialgroove between the lift plate 108 and the lower bellows flange 92 b.Actuation of the lift actuator 104 causes the bellows assembly 92 tomove between a compressed upper position (not shown) and a relaxed lowerposition (FIGS. 2-3).

[0025] The pedestal 18 includes a longitudinal central bore 72 cextending through the shaft 72 and plate 74. The chuck 16 is mounted tothe top of the plate 74 and cooperates with the plate 74 to define acoolant chamber 100. A plurality of slots 16 a formed in the face of thechuck 16 are in fluid communication with the chamber 100. A spiderassembly 102 includes a spider 102 a disposed in the coolant chamber 100and a hollow lift rod 102 b disposed in the central bore 72 c. As thebellows assembly 92 moves in response to actuation of the lift actuator104, the push rod 102 b moves between a wafer unloading position,corresponding to the compressed position of the bellows assembly 92, anda wafer clamping position, corresponding to the relaxed position of thebellows assembly 92.

[0026] A rotational coupler 114 couples a helium source (not shown) tothe lower bellows flange 92 b and the pedestal 18. The rotationalcoupler 114 is coupled to a vented screw 116 that allows helium to passfrom the rotational coupler 114 to the hollow lift rod 118. Thus, therotational coupler 114 and the vented screw 116 move with the lift rod118 in response to actuation of the lift actuator 104. The lift rod 118conveys helium to the coolant chamber 100 and the slots 16 a.

[0027] The dome 30 includes an upper electrode 128. The upper electrode128 includes a gas inlet 130 and a header 132 formed to include aplurality of gas outlets 134. Preferably, the upper electrode 128 ismade of a conductive material such as aluminum having an anodic oxidesurface. The upper electrode 128 faces the chuck 16 which serves as alower electrode. The lower electrode 16 is grounded and an RF source 138(FIG. 1) is applied to the upper electrode 128 and provides energy tothe interior region 32 to ionize the gas and form the plasma for etchingthe wafer.

[0028] A representative plasma etching process is illustrated in FIG. 4.A wafer is loaded into the process chamber 12 and the machine 201 isstarted at step 201 to begin the process. Based on a predefined process,a controller 131 establishes process parameters. Initially, thecontroller 131 establishes a gas flow into the process chamber 12 atstep 204. The gas enters through the gas inlet 130 and passes out of theheader 132 through the outlets 134 into the process chamber 12. Thecontroller 131 continues the gas flow 204 to establish a chamberpressure at a set point during step 206. Depending on the processinvolved, the gas flow can vary from less than 1 SCCM to a few SLM andthe pressure can vary from a few millitorr to 2.5 torr and beyond.

[0029] The controller 131 also establishes backside cooling of the chuck16 in step 208 by sending helium through the rotational coupler 114 andpush rod 102 b to the coolant chamber 122 and allows the temperature tostabilize. The controller 131 also energizes the ELECTROSTATIC BIASROLLER 96 to electrostatically charge the chuck 16 in step 210 andsignals the drive motor 20 to begin pedestal rotation at a predeterminedRPM at step 212. When all of the process parameters are stabilized, thecontroller 131 activates RF power by energizing the RF source 138 togenerate the etching plasma at step 214. Power settings can vary,depending on the process involved, from a few watts to an excess of 2megawatts. When the plasma is generated, the process continues until theexpiration of a pre-set time or an end point occurs at step 218. At thatpoint, the controller 131 stops the process, stopping the chuckrotation, rotating the chuck to the unload position, and deenergizingthe RF source during step 220. The controller 131 also stops the gasflow at step 222 and returns the pressure, backside cooling, andelectrostatic voltage to the idle state at steps 224, 226, 228,respectively. When the system is returned to the idle state, thecontroller 131 unloads the wafer at step 230 by signaling the liftactuator 104 to push up on the lift plate 108. The lift plate 108, inturn, pushes on the lift rod 102 b and the spider 102 a, which contactsthe wafer and lifts the wafer from the chuck 16. At that point, duringstep 230, a new wafer can be loaded into the process chamber 12 and theprocess repeated, or the process can be terminated, as at step 232.

[0030] The present invention has been described with reference to anelectrostatic chuck. It will be appreciated by those of ordinary skillin the art that a mechanical clamp can be used, although it is notpreferred. A mechanical clamp adds more mass to the rotating pedestaland must be carefully machined to ensure that it is balanced about therotational axis of the pedestal.

[0031] The above descriptions and drawings are only illustrative of thepreferred embodiments which present the features and advantages of thepresent invention, and it is not intended that the present invention belimited thereto. Any modification of the present invention which comeswithin the spirit and scope of the following claims is considered partof the present invention.

What is claimed as new and desired to be protected by Letters Patent ofthe U.S. is:
 1. A chuck assembly for use with a semiconductor waferplasma etching device, the assembly comprising: a chuck; a pedestalcoupled to the chuck and having a longitudinal axis; and a drive motorcoupled to the pedestal for rotating the pedestal about the longitudinalaxis.
 2. A chuck assembly comprising: an internally cooled chuck; aclamp coupled to the chuck; a pedestal coupled to the chuck and having acentral bore and a longitudinal axis, the chuck and pedestal cooperatingto define a coolant chamber that communicates with the central bore; anda drive motor coupled to the shaft for rotating the shaft about thelongitudinal axis.
 3. The assembly of claim 2 wherein the clamp includesan electrostatic clamp.
 4. The assembly of claim 3 wherein theelectrostatic clamp includes an electrostatic bias roller disposed incontact with the shaft.
 5. The assembly of claim 2 further comprising aspider disposed in the coolant chamber and a push rod coupled to thespider and disposed in the central bore, the push rod including acoolant passage in communication with the coolant chamber.
 6. A chuckassembly for use with a plasma etching device, the assembly comprising:a chuck including a top surface having a plurality of slots; a pedestalcoupled to the chuck and defining therewith a coolant chamber incommunication with the slots, the pedestal having a longitudinallyextending passage in fluid communication with the coolant chamber, thepedestal being rotatable about a longitudinal axis; a plurality of liftpins disposed in the coolant chamber and coupled to a longitudinallyextending push rod disposed in the pedestal, the push rod including acoolant passage in communication with the coolant chamber; and anelectrostatic clamp including an electrostatic voltage source coupled tothe shaft.
 7. The assembly of claim 6 further including a bellowsassembly coupled to the pedestal and a lift actuator coupled to thebellows assembly, the push rod moving between a wafer unloading positionand a wafer clamping position and the bellows moving between acompressed position and a relaxed position in response to movement ofthe lift actuator.
 8. The assembly of claim 7 further including arotational coupler coupled to the push rod and a source of coolant, therotational coupler moving with the push rod in response to actuation ofthe lift actuator.
 9. The assembly of claim 6 further including a blockcoupled to a process chamber, the pedestal being coupled to the blockfor rotation therein, the block including a plurality of bearings forsupporting the pedestal during rotation and a plurality of seals, theseals cooperating with the pedestal to seal the process chamber.
 10. Amethod for plasma etching wafer comprising the steps of: coupling achuck to a pedestal; coupling the wafer to the chuck; rotating thepedestal; and plasma etching the wafer while the pedestal is rotating.11. The method of claim 10 further comprising the steps of internallycooling the chuck.
 12. The method of claim 11, wherein the pedestalcooperates with the chuck to define a coolant chamber and includes ashaft having a coolant passage in communication with the coolantchamber, the step of internally cooling further including the step ofintroducing coolant to the coolant chamber through the coolant passage.13. The method of claim 10 wherein the pedestal includes a push rodhaving a coolant passage, the coolant passage being in communicationwith a coolant source and a coolant chamber defined by the chuck and thepedestal.
 14. The method of claim 10 wherein the chuck includes anelectrostatic clamp.
 15. The method of claim 10 further comprising thesteps of initializing process parameters, the process parametersincluding gas flow, process chamber pressure, water temperature, andpedestal rotation speed.
 16. The method of claim 10 further includingthe step of unloading the wafer from the chuck after plasma etching, theunloading step including the steps of providing a lift actuator coupledto a push rod and a spider and actuating the lift actuator, the push rodpushing the spider to move the wafer away from the chuck in response toactuation of the lift actuator.
 17. A plasma etching machine comprising:a process chamber; a rotatable, internally cooled chuck disposed in theprocess chamber, and a controller coupled to the process chamber andchuck for controlling gas flow and pressure in the process chamber androtation of the chuck.
 18. The machine of claim 17 further comprising apedestal coupled to the chuck and cooperating therewith to define acoolant chamber, the pedestal including a coolant passage in fluidcommunication with a coolant source and the coolant chamber.
 19. Themachine of claim 18 further including a lift actuator coupled to thecoolant passage, the coolant passage moving in the pedestal in responseto actuation of the lift mechanism to lift a wafer from the chuck. 20.The machine of claim 17 further including a pedestal coupled to thechuck, a block coupled to the process chamber, the pedestal beingdisposed in the block for rotation therein, and a bellows assemblycoupled to the pedestal, the block, pedestal, and bellows assemblycooperating with each other to seal the process chamber.
 21. A plasmaetching machine comprising: a process chamber; a chuck disposed in theprocess chamber; a pedestal coupled to the chuck and cooperatingtherewith to define a coolant chamber, the pedestal including a coolantpassage in communication with the coolant chamber; a drive motor coupledto the pedestal for rotating the pedestal during plasma etching.
 22. Themachine of claim 21 further comprising a bellows assembly coupled to thepedestal and to a source of coolant, and a lift mechanism coupled to thebellows assembly, the lift mechanism including a lift plate coupled to apush rod disposed in the pedestal, the push rod including the coolantpassage and being coupled to a plurality of lift pins, the lift pinslifting a wafer from the chuck in response to movement of the liftplate.
 23. A plasma etching machine comprising: a process chamberdefining an interior region and including a bottom wall having anaperture; a block disposed in the aperture and including alongitudinally extending bore; a shaft extending through the bore andincluding a spider push rod extending longitudinally therethrough, theshaft being supported for rotation in the bore; a chuck coupled to theshaft and disposed in the interior region, the chuck cooperating withthe shaft to define a coolant chamber; a spider disposed in the coolantchamber and coupled to the spider push rod; a lift mechanism coupled tothe spider push rod, the spider pushing up on a wafer in response toactuation of the lift mechanism; and a drive motor coupled to the shaftfor rotating the shaft during a plasma etching process.
 24. The machineof claim 23 wherein the block includes a plurality of bearings forsupporting the shaft for rotation in the block and a plurality of sealsfor sealing the process chamber.
 25. The machine of claim 23 furthercomprising a bellows assembly coupled to the shaft and to a coolantsource, the lift mechanism including a lift plate coupled to the bellowsassembly, the lift plate and bellows assembly being movable between awafer lifting position and a disengaged position, the spider push rodincluding a coolant passage in communication with the chamber and beingmovable in response to movement of the lift plate and bellows assembly.